question

victron avatar image
victron asked

MultiPlus reported amps under reported when generator running.

I'm running two MulitPlus 24/3000/70-50 120V in parallel. firmware v482.
When the multis inverting the AC-OUT Watts is close enough (+- a few percent) to V*A = W.
With Honda EU2200i generator running:
AC IN: rough average V*(A*1.6) = W
AC OUT: rough average V*(A*2.56) = W

Input limit: 5.0A
Overruled by remote: Off

Inverter Power Assist: Off

With generator running
AC IN 1:
Voltage: 120
Current: 9.5 (15.2\9.5=1.6)
Power: 1826W
Frequency: 60.3Hz

AC OUT L1:
Voltage: 120
Current: 3.8A (9.725\3.8)=2.56)
Power: 1167W
Frequency: 59.9Hz

Battery:
Voltage: 26.69V
Current: 22A

As long as I set the Input limit to 1/3 of what I want the maximum watts pulled from the generator, it won't overload the generator. Setting it at 4.3A in general ensures it never pulls much more than 1,800W. At 5W it will creap up towards 1,900W and bounce between there and 2,100W at 120V.

I did measure same length 5' (1.5M) and torque down the 6 AWG(13.3mm2) THHN copper from busbar to the two Multi's the same. However, amp meter shows load is different about 1:3 between the two Multi's. Wondering if that mismatch in load is the cause of my issues? Unsure what to do other than maybe change out the THHN wire to Ancor Marine 266 strand tin coated copper.

Just so strange that the AC OUT L1 current is so far off when in passthru vs. inverting.

Thanks in advance for any ideas.

multiplus in parallel
1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

victron avatar image victron commented ·

Just a quick follow up. Not sure how, but the configuration of the parallel MultiPlus's may have been corrupt. (I trust Victron enough to know it must have been self inflicted.) I configured a backup MultiPlus after updating the firmware and it configured and behaved correctly. Probably should have just reset to factory defaults in production and rebuilt, but had the 'spare' twin to test on so I did.


Saved the configuration from the properly behaving Multi, and used it on the master of the parallel Multi's. That instanly displayed double the programmed input limit from 15 to 30 (change from '2' no matter what I had). Hope to test functionality this weekend.


0 Likes 0 ·
2 Answers
Mike Dorsett avatar image
Mike Dorsett answered ·

An on line converter is giving 6AWG as 13mm^2 which would have a current rating of about 70A!! for 2.5kW @110V, the current should be about 22A - for this I would use 2.5mm^2 for short distances - this would translate as 13AWG. This will carry the current, and give you higher resistance for better balance.

The DC cables need to carry 125A each, and need to be a minimum of 35mm^2 or 1AWG as this is the next largest size.

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

victron avatar image victron commented ·

Palm > Forehead (Thank you!)

I do recall reading Multis work off the ratio of resistance when I installed them a couple years ago.

I've been building up the battery bank lately where you want the exact opposite. Counterintuitive enough to make inbound generator power less efficient I didn't even think to go back to the manual. Second time I failed to consult the manual in three years during a system redesign. Hopefully this time I'll finally learn my lesson.

I'm also lazy. I didn't want to haggle with the inspector over the fact I'm not going to move 50 amps in per MultiPlus and therefore don't require at least 63A capacity. (Code requires adjustment factor of 1.25 since they'd carry current more than 3 hours continuously.) Use the leftover wire, I told myself. Avoid the long argument with the inspector.

I'm running 6 foot factory build 2/0AWG (70mm2) wire from the Multis to a 1000A DC bus bar, so shouldn't be issues there. I will re-test impedance on them tonight while running on battery. Nothing has changed there except time in service, so worth a check.

Not really a big deal since I only run the genny 5-10 days a year in winter recently. The mismatch isn't going to super stress one Multi over the other.

I'll play again after fire season. We're already in fire weather watches, so I'm not going to run the generator unless there's a dire emergency. I might look into inline resistors to avoid running a bunch of extra wire in the wire way trying to make things even (hotter).

0 Likes 0 ·
Mike Dorsett avatar image
Mike Dorsett answered ·

I'm running 2 x 1200/24's in parallel, and they share the generator load fairly equally. However, the charge limit set on both inverters is 1/2 of the load amps on the generator. There is some difference in the AC cable resistance between the two, but like you I have the DC cables to a bus-bar, and they are equal. I found That I had to set the battery charge current limit, and leave the AC input current limit at 16A for stable operation (otherwise the fridge switch on surge knocked the system out of charge). I have a smart energy meter on the AC output of each inverter before they are combined, so can monitor the reverse power flow into the AC out of the slave inverter during generator charging. Are you able to measure the DC current reported / actual from each inverter? I'm also not clear on your current calculations during charging?

2 comments
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Mike Dorsett avatar image Mike Dorsett commented ·
BTW my system voltage is 240 not 120, but that should not make a difference to the operation.
0 Likes 0 ·
victron avatar image victron Mike Dorsett commented ·

Actually, I have the generator attached to two bus bars (neutral and line). The difference between the AC 'load' is between the generator and AC IN L1 on Multi 1 and Multi 2. I can only tell there's a difference between the two Multi's is by putting a clamp on the AC L1 lines between the two Muli's on the bus bars.

The manual says the AC lines must have exactly the same resistance between the two. On such short runs I'm concerned even a fraction of an inch could be causing the Multi's to invert at different rates.

I've ordered 6AWG 266 strand cable (0.4 Ohms per 1,000 meters) and will replace the THHN to see if that makes any difference on the input from Generator to Multi. I'll also ensure the wires are less than 1/4" difference between them. My multimeter probably isn't accurate enough to reliably detect the resistance difference between the two Multi's and the generator bus bars.

With luck the lower resistance will help the Multi's to operate at the same inversion\passthru rates. (0.000004 ohms between consuctors will hopefully be close enough.)

0 Likes 0 ·